rest. As is
well known, the submarine campaign reached its climax in April, 1917.
In that month British and Allied shipping sustained its greatest
losses. The value of the airship in combating this menace was now fully
recognized, and with the big building programme of Zero airships
approved, the housing accommodation again reached an acute stage.

Shortage of steel and timber for shed building, and the lack of labour
to erect these materials had they been available, rendered other
methods necessary. It was resolved to try the experiment of mooring
airships in clearings cut into belts of trees or small woods.

A suitable site was selected and the trees were felled by service
labour. The ships were then taken into the gaps thus formed and were
moored by steel wires to the adjacent trees. Screens of brushwood were
then built up between the trees, and the whole scheme proved so
successful that even in winter, when the trees were stripped of their
foliage, airships rode out gales of over 60 miles per hour. The
personnel were housed either in tents or billeted in cottages or houses
in the neighbourhood, and gas was supplied in tubes as in the earlier
days of the stations before the gas plants had been erected.

This method having succeeded beyond the most sanguine expectations,
every station had one or more of these sub-stations based on it, the
airships allocated to them making a periodical visit to the parent
station for overhaul as required. Engineering repairs were effected by
workshop lorries, provided that extensive work was not required.

In this way a large fleet of small airships was maintained around our
coasts, leaving the bigger types of ships on the parent stations, and
the operations were enabled to be considerably extended. Of course,
certain ships were wrecked when gales of unprecedented violence sprung
up; but the output of envelopes, planes and cars was by this time so
good that a ship could be replaced at a few hours' notice, and the cost
compared with building of additional sheds was so small as to be
negligible.

From the month of April, 1917, the convoy system was introduced, by
which all ships on entering the danger zones were collected at an
appointed rendezvous and escorted by destroyers and patrolboats. The
airship was singularly suitable to assist in these duties. Owing to
her power of reducing her speed to whatever was required, she could
keep her station ahead or abeam of the convoy